1. Field of the Invention
The present invention relates to a so-called .beta. azimuth magnetic head whose magnetic-gap forming faces and tape rubbing surfaces of a single-crystal ferrite core are allowed to coincide with the (100) plane and the (110) plane, respectively, and particularly, relates to a magnetic head having improved magnetic permeability and head output in a high frequency range of not less than 10 MHz.
2. Description of the Related Art
FIG. 10 is a perspective view of a magnetic head, and FIG. 11 is an enlarged plan view of the same viewed from rubbing surfaces to be in contact with a recording medium.
A pair of core halves 1 are made of a single-crystal ferrite composed of Fe.sub.2 O.sub.3, MnO, and ZnO, or a jointing material of a single ferrite and a poly-crystal ferrite. The pair of core halves 1 are joined together with a non-magnetic material interposed therebetween to form a magnetic gap G. Magnetic-gap forming faces 1a and a track width Tw' are also shown in FIG. 11.
Each of the core halves 1 has tapered faces (i.e., track width defining faces) 1b inclined with respect to the magnetic-gap forming face 1a. Glass 2 fills the region formed by the tapered faces 1b so as to join the magnetic-gap forming faces 1a of the core halves 1. The core halves 1 have coils 3 for recording and reproducing. Although the azimuthal angle of the magnetic gap G is 0 in FIG. 10, in practice, the magnetic gap G has a certain azimuthal angle clockwise or counterclockwise with respect to the magnetic circuit direction shown in FIG. 11.
Crystals of the ferrite materials have a cubic structure, and the magnetic head shown in FIG. 10 is a so-called .beta. azimuth magnetic head whose magnetic-gap forming faces and the tape rubbing surfaces are in the crystallographic planes of the ferrite designated by (100) and (110). The crystallographic axis along the magnetic circuit direction on the tape rubbing surfaces is in the &lt;100&gt; direction. Rubbing surfaces of .beta. azimuth magnetic heads must have excellent wear resistance.
The crystallographic axis &lt;100&gt; is an easy axis of magnetization when the magnetocrystalline anisotropic energy Kl, determined by the composition of a single-crystal ferrite, is more than 0, while the crystallographic axis &lt;100&gt; is a hard axis of magnetization when the magnetocrystalline anisotropic energy Kl is less than 0. The closer the absolute value of the magnetocrystalline anisotropic energy Kl approaches 0, the lower the magnetic anisotropy becomes.
Conventionally, in such types of magnetic heads, the magnetocrystalline anisotropic energy Kl is generally set to a value as close as possible to 0 to achieve a higher permeability because the permeability is in inverse proportion to the magnetocrystalline anisotropic energy Kl.
In addition, ferrite materials exhibit magnetostriction, and the saturation magnetostriction .lambda.S of a ferrite material as a whole is determined by its composition. Similar to the above-mentioned the magnetocrystalline anisotropic energy Kl, the saturation magnetostriction .lambda.S is in inverse proportion to the permeability. Therefore, it has been considered that a higher permeability can be also achieved by setting the saturation magnetostriction .lambda.S to a value as close as possible to 0.
FIG. 3 is a ternary diagram showing compositions of a ferrite material composed of Fe.sub.2 O.sub.3, MnO, and ZnO. The magnetocrystalline anisotropic energy Kl and the saturation magnetostriction .lambda.S are both near 0 in a ferrite material composed of 51 to 56 mol % of Fe.sub.2 O.sub.3, 27 to 32 mol % of MnO, and 12 to 22 mol % of ZnO. These ranges correspond to the region I in the figure. Cores of conventional magnetic heads have been made of a single-crystal ferrite having a composition within the region I.
However, when a magnetic head, made of a single-crystal ferrite having a composition within the region I in which the magnetocrystalline anisotropic energy Kl and the saturation magnetostriction .lambda.S are were both near 0, had magnetic-gap forming faces 1a each having an area of not more than 300 .mu.m.sup.2 and a narrow track width Tw', the recording and reproducing outputs of the magnetic head were reduced at a high frequency such as several MHz to 10 MHz.
This phenomenon is attributed to the following: in the magnetic head having such small magnetic-gap forming faces 1a, the effects of the residual stress due to processing the core halves 1 and the stress caused by a difference between the coefficients of thermal expansion of the glass 2 and the ferrite are so great that the magnetoelastic energy, which is in proportion to the product of the magnetostriction .lambda. and the stress .sigma., correspondingly increases; thus the permeability of the single-crystal ferrite of the magnetic-gap forming portions practically deteriorates. In addition to the above, the permeability significantly deteriorates at a high frequency because the magnetic circuit direction of the magnetic-gap forming portions becomes an easy axis of magnetization.